In highly accurate spirit levels, it is necessary to true the level element very precisely with respect to the reference surface and/or measuring surface of the housing using adjusting means. Only in the case of low precision spirit levels is it adequate, following truing, to fix the level element by means of small wedges inserted between the level element and a housing cavity by pouring a rapidly solidifying material, e.g. gypsum or liquid sulphur into the gap between the ends of the level element and the housing cavity. In order to permit a fine adjustment, hitherto tubular level elements have been arranged in a metallic sleeve member and have been fixed in it by grouting, followed by the subsequent insertion in a hole in the housing and radial truing by adjusting means. The diameter of the hole in the housing must be that much larger than the external diameter of the sleeve member to permit such a radial adjustment. The adjusting means comprise, for example, at least three set screws which, with the same angular distance from one another, enclose a sleeve end between them. By turning the set screws, provided with a fine thread, a radial adjustment of the end of the sleeve member in the direction of the particular radially directed set screw being actuated is obtained and the sleeve member rotates about its facing end, so that the angle can be varied to such an extent relative to the reference surface of the housing until the level element axis is precisely parallel or vertical to said reference or measuring surface. A similar adjusting possibility can be provided on the opposite end of the sleeve member if there is no centering mounting support there.
Adjustment by means of set screws acting on at least three peripheral points of the sleeve member has the disadvantage that the magnitude of the force produced by the set screw is uncontrolled. Deformation of the sleeve occurs and the relationship between elastic and plastic deformation, partly also on the sleeve surface, changes after a certain time, particularly due to vibrations so that the precision of the spirit level does not remain constant. As a result of the imprecise magnitude of the forces which occur, it is, in particular, not possible to do away with a sleeve member enclosing the level element, because the generally glass level elements can only absorb local pressures.